The present invention relates to improvements in shaft preheaters for rotary kilns or the like, and more particularly to an improved shaft preheater capable of preheating two different lime fractions of different grain size.
The shaft preheater has an arrangement wherein more coarse and more fine limestone materials are introduced into the upper end of a preheating chamber with the lower end of the preheating chamber discharging to the kiln.
In the arrangements of shaft preheaters of the general above referred to type, it has been heretofore been not possible to utilize transverse flows of heating gas directed into the upper portion of the shaft preheater to equally heat different material fractions. In conventional arrangements, when the coarse material fraction enters the preheater at an inner location, the hot gases which contact the coarse material have already cooled off after passage through the outer fine fraction. The result of this is that the outer fine fraction is precalcined and the inner coarse fraction receives too small a portion of the quantity of heat available so that as the material enters the rotary kiln, a further heating of the coarse fraction must first take place before it is calcined.